Hello and Thanks.

I have a problem I believe to be a MAP or the SD computer. The haines book says there are two diff types of MAP's. Voltage and RPM(FREQ) . It tells me
I should have 4-6 VDC ref. I do on the 3rd pin from the grill going left to right.
It tell me for the voltage type key on engine not running I should get ablut 5VDC on the second wire. I got 2.5VDC. Say about 70 % load. This makes it flood and will only run with WOT and release key it dies. So I jumped pin 3 to 2. Forced 5VDC to teh second pin. Truck starts and runs and acts lean as I would expect. Have to throttle to keep running. A new MAP is $55. Sent my son to the junk yard. (his truck) Same thing with junk yard map. Original one I sucked on the vac line and the voltage stayed at 2.5 VDC. Did not test the different one. So the computer sees the jumper which tells me the wires are good. Anyone have resistance checks for this type of MAP? I can also see the computer putting out a ground causing the MAP to be a voltage divider. Seems it should be an input and if it failed could also cause this.
I know the junk yard map is not a known good part. I checked into computer and the numbers on them are many and confusing... I am not sure but it seems to me 87-92's use voltage maps and 93 up use RPM. Is that correct?
Anyone have a schematic of the computer or resistant checks on the maps and the 3 wires to ground on a good running truck? Any input would be appreciated!

Thanks!

 

You have a frequency varying MAP sensor (as do all the 87-96 F-series trucks I've worked on). No matter what the frequency, the voltage on the center pin will always read 2.5V (the MAP sensor switches between the high and low voltage, just at varying frequencies such that the average is always half way between the high and low voltage reference wires, 0V and 5V in this case, no matter what frequency signal is being generated). You need to test it with either a tachometer or a multimeter on the frequency scale. I hope you didn't jumper the 5V to the signal wire with the MAP sensor attached, as you may have ruined it. The reason it ran while jumpered is probably because the computer went into limp mode.

 

www.ford fuelinjection.com
go here and read
they have all the test procedures
lots of great info on sensors

 

Thanks all. You got me back on the right track with the MAP. The Haines Man. kind of put me in the wrong direction. Easy enough. So the MAP checked out good. Pretty much leaves me only left with the ECM. Seems there are about 400 diff ones. Is there a place I can cross ref parts to check the junk yard or ebay? My number off mine is E9TF-12a650-ARA. I have searched the internet for 5 days now trying to gather info in ECM. I removed mine to inspect the caps on it and they are good. So anyone good ECM info/links? Thanks!